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Publication numberUS8089326 B2
Publication typeGrant
Application numberUS 12/605,436
Publication dateJan 3, 2012
Filing dateOct 26, 2009
Priority dateOct 26, 2009
Also published asUS20110095831
Publication number12605436, 605436, US 8089326 B2, US 8089326B2, US-B2-8089326, US8089326 B2, US8089326B2
InventorsMeng-Chih Weng
Original AssigneeHimax Technologies Limited
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
PVT-independent current-controlled oscillator
US 8089326 B2
Abstract
The invention discloses a PVT-independent current-controlled oscillator, including a PV-controller, a current-controlled oscillator and a T-controller. The current-controlled oscillator is coupled to the PV-controller and outputs an oscillation frequency. The T-controller is coupled to the PV-controller and the current-controlled oscillator, providing a total current to be shared by the PV-controller and the current-controlled oscillator, wherein the PV-controller decreases the shared current of the current-controlled oscillator by increasing the shared current of the PV-controller if the oscillation frequency is higher than a predetermined frequency due to a process variation of the current-controlled oscillator, and increases the shared current of the current-controlled oscillator by decreasing the shared current of the PV-controller if the oscillation frequency is lower than the predetermined frequency due to the process variation of the current-controlled oscillator, thereby dynamically adjusting the oscillation frequency.
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Claims(9)
1. A PVT-independent current-controlled oscillator, comprising:
a PV-controller, the current of the PV-controller is intentionally made a function of the process and supply voltage variations;
a current-controlled oscillator coupled to the PV-controller and outputting an oscillation frequency; and
a T-controller coupled to the PV-controller and the current-controlled oscillator, providing a total current to be shared by the PV-controller and the current-controlled oscillator,
wherein the current of the T-controller is intentionally made a function of temperature deviation, and the PV-controller decreases the shared current of the current-controlled oscillator by increasing the shared current of the PV-controller if the oscillation frequency is higher than a predetermined frequency due to a process variation of the current-controlled oscillator, and increases the shared current of the current-controlled oscillator by decreasing the shared current of the PV-controller if the oscillation frequency is lower than the predetermined frequency due to the process variation of the current-controlled oscillator, thereby dynamically adjusting the oscillation frequency.
2. The PVT-independent current-controlled oscillator as claimed in claim 1, wherein the T-controller comprises:
a bandgap circuit generating a first bandgap voltage and a second bandgap voltage and a bandgap current, wherein the bandgap current is generated from the first bandgap voltage;
a first regulator circuit generating a regulator current according to the second bandgap voltage;
a pair of PMOS transistors generating a temporary total current according to the regulator current and the bandgap current; and
a second regulator circuit generating the total current according to the temporary total current.
3. The PVT-independent current-controlled oscillator as claimed in claim 2, wherein the PV-controller comprises:
a third regulator circuit receiving the first bandgap voltage and dividing the first bandgap voltage into a divided voltage; and
an adjust circuit coupled to the third regulator circuit, receiving the total current, and adjusting the magnitude of the current of the PV-controller shared from the total current according to the divided voltage.
4. The PVT-independent current-controlled oscillator as claimed in claim 3, wherein, when the current-controlled oscillator comprises a PMOS transistor, the adjust circuit comprises:
a PMOS transistor having a source coupled to the first bandgap voltage, and a gate coupled to the divided voltage; and
a current mirror coupled to the PMOS transistor, wherein the magnitude of the current of the PV-controller shared from the total current is higher when the current of the PMOS transistor is increased, and the magnitude of the current of the PV-controller shared from the total current is lower when the current of the PMOS transistor is decreased.
5. The PVT-independent current-controlled oscillator as claimed in claim 3, wherein, when the current-controlled oscillator comprises an NMOS transistor, the adjust circuit comprises:
an NMOS transistor having a drain coupled to the total current, a gate coupled to the divided voltage, and a source coupled to a ground, wherein the magnitude of the current shared from the total current is higher when the current of the NMOS transistor is increased, and the magnitude of the current shared from the total current is lower when the current of the NMOS transistor is decreased.
6. The PVT-independent current-controlled oscillator as claimed in claim 3, wherein the third regulator circuit comprises:
an operational amplifier having a first input receiving the first bandgap voltage, a second input and an output;
a PMOS transistor having a gate coupled to the output of the operational amplifier, a source coupled to a power supply and a drain coupled to the second input; and
a resistor coupled between the drain and a ground.
7. The PVT-independent current-controlled oscillator as claimed in claim 2, wherein the first regulator circuit comprises:
an operational amplifier having a first input receiving the second bandgap voltage, a second input and an output;
a PMOS transistor having a gate coupled to the output, a source coupled to a power supply and a drain coupled to the second input; and
a resistor coupled between the drain and a ground,
wherein the magnitude of the regulator current is the second bandgap voltage divided by the resistance of the resistor.
8. The PVT-independent current-controlled oscillator as claimed in claim 2, wherein the pair of PMOS transistors comprises:
a first PMOS transistor having a first gate coupled to the bandgap circuit, a first source coupled to a power supply, and a first drain; and
a second PMOS transistor having a second gate coupled to the first regulator circuit, a second source coupled to the power supply, and a second drain coupled to the first drain for providing the temporary total current.
9. The PVT-independent current-controlled oscillator as claimed in claim 2, wherein the second regulator circuit comprises:
a resistor having a first end coupled to the pair of PMOS transistors, and a second end coupled to a ground.
an operational amplifier having a first input coupled to the first end of the resistor, a second input and an output;
a first PMOS transistor having a first gate coupled to the output, a first source coupled to a power supply, and a first drain coupled to the second input;
a second PMOS transistor having a second gate coupled to the first gate, a second source coupled to the power supply, and a second drain coupled to the current-controlled oscillator and the PV-controller for providing the total current thereto; and
a high-precision resistor coupled between the first drain and the ground.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a current-controlled oscillator (CCO), and more particularly, to a current-controlled oscillator that is not affected by process variation, supply voltage variation, and temperature deviation.

2. Description of the Related Art

A current-controlled oscillator is an electronic oscillator designed to generate an oscillation frequency through the control of current. However, similar to most electronic components, the performance of a current-controlled oscillator is often affected by various factors such as process variation, supply voltage variation, and temperature deviation (also called PVT hereinafter). Referring to FIG. 1, an illustrative diagram of a current-controlled oscillator is shown. In FIG. 1, the current-controlled oscillator 10 is designed to generate an oscillation frequency Fout, which may be adjusted by the current source IC. However, although having a fixed current source IC, the oscillation frequency Fout that is output is still varied due to PVT.

FIG. 2 depicts a characteristic curve of a current-controlled oscillator. It is clearly shown in FIG. 2, that the oscillation frequency Fout output from the current-controlled oscillator 10 is inversely related to temperature, which is undesired for an ideal current-controlled oscillator.

BRIEF SUMMARY OF THE INVENTION

In light of the previously described problems, a current-controlled oscillator that is not affected by process variation, supply voltage variation, and temperature deviation is provided.

An embodiment of the invention discloses a PVT-independent current-controlled oscillator, comprising a PV-controller, a current-controlled oscillator and a T-controller. The current-controlled oscillator is coupled to the PV-controller and outputs an oscillation frequency. The T-controller is coupled to the PV-controller and the current-controlled oscillator, providing a total current to be shared by the PV-controller and the current-controlled oscillator, wherein the PV-controller decreases the shared current of the current-controlled oscillator by increasing the shared current of the PV-controller if the oscillation frequency is higher than a predetermined frequency due to a process variation of the current-controlled oscillator, and increases the shared current of the current-controlled oscillator by decreasing the shared current of the PV-controller if the oscillation frequency is lower than the predetermined frequency due to the process variation of the current-controlled oscillator, thereby dynamically adjusting the oscillation frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 depicts an illustrative diagram of a current-controlled oscillator;

FIG. 2 depicts a characteristic curve of a current-controlled oscillator;

FIG. 3 depicts a diagram of a PVT-independent current-controlled oscillator according to an embodiment of the invention;

FIG. 4 depicts a circuit diagram of a T-controller according to an embodiment of the invention;

FIG. 5A depicts a full circuit diagram of a PV-controller according to an embodiment of the invention;

FIG. 5B depicts a circuit diagram of a partial PV-controller according to an embodiment of the invention; and

FIG. 5C depicts a circuit diagram of a partial PV-controller according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

FIG. 3 depicts a diagram of a PVT-independent current-controlled oscillator according to an embodiment of the invention. The PVT-independent current-controlled oscillator 30 comprises a temperature controller (T-controller) 31, a process and voltage controller (PV-controller) 32 and a current-controlled oscillator 10. The T-controller 31 provides a voltage VN1 to the PV-controller 32 and a current IM6 to be shared by the PV-controller 32 and the current-controlled oscillator 10. In addition, the T-controller 31 prevents the current-controlled oscillator 10 from being affected by temperature deviations and the PV-controller 32 prevents the current-controlled oscillator 10 from being affected by the process and supply voltage variations, thereby enabling the current-controlled oscillator 10 to output an oscillation frequency that is not affected by process variation, supply voltage variation, and temperature deviation (PVT).

FIG. 4 depicts a circuit diagram of a T-controller according to an embodiment of the invention. The T-controller 31 comprises a bandgap circuit 310, a first regulator circuit 312, a PMOS transistors pair 314 and a second regulator circuit 316. The bandgap circuit 310 generates a first bandgap voltage VN1 that is not affected by PVT, a second bandgap voltage VN4 that is inversely proportional to the temperature (the higher the temperature the lower the second bandgap voltage VN4), and a bandgap current IN1. The first regulator circuit 312 comprises an operational amplifier, a PMOS transistor M2 and a resistor R1. The operational amplifier has a first input, a second input and an output. The first input receives the second bandgap voltage VN4. The second input is coupled to one end of the resistor R1and the drain of the PMOS transistor M2. The output of the operational amplifier is coupled to the gate of the PMOS transistor M2. The source of the PMOS transistor M2 is coupled to the power supply. Another end of the resistor R1 is coupled to the ground. The PMOS transistors pair 314 has a PMOS transistor M4 and a PMOS transistor M3. The PMOS transistor M4 has a gate coupled to the gate of the PMOS transistor M1 of the bandgap circuit 310, a source coupled to the power supply, and a drain. The PMOS transistor M3 has a gate coupled to the gate of the PMOS transistor M2 of the first regulator circuit 312, a source coupled to the power supply, and a drain coupled to the drain of the first PMOS transistor M4. The second regulator circuit 316 comprises a resistor R2, an operational amplifier, a PMOS transistor M5, a PMOS transistor M6 and a high-precision resistor Rext. The resistor R2 has a first end coupled to the PMOS transistors pair 314, and a second end coupled to the ground. The operational amplifier has a first input coupled to the first end of the resistor R2, a second input and an output. The first PMOS transistor M5 has a gate coupled to the output of the operational amplifier, a source coupled to the power supply, and a drain coupled to the second input of the operational amplifier. The PMOS transistor M6 has a gate coupled to the gate of the PMOS transistor M5, a source coupled to the power supply, and a drain coupled to the current-controlled oscillator 10 and the PV-controller 32. The high-precision resistor is coupled between the drain of the first PMOS transistor M5 and the ground.

In the bandgap circuit 310, if the voltage VN2 is equal to the second bandgap voltage VN4, then the following equation will be satisfied:
I MA R A +V EB1 =V EB2

Therefore,
I MA *R A =V BE1 −V BE2

wherein,

V BE 1 = V T ln n I MA I S 1 , V BE 2 = V T ln n I N 1 I S 2 .

Therefore,
I MA *R A =V T ln(n).

Based on this, if three MOS transistors MA, MB and M1 are the same, then:

V N 1 = ( V T ln ( n ) R A ) * R B + V EB 3 .

Wherein, the bandgap current IN1 is determined to be (VT*ln(n)/RA), which is proportional to the temperature. Since the gate of the PMOS transistor M1 is connected to the gate of the PMOS transistor M4 and the source of the PMOS transistor M1 is also connected to the source of the PMOS transistor M4, the bandgap current IN1 reflects the current IM4 on the PMOS transistor M4. The reflected current IM4 may or may not be the same as the bandgap current IN1, depending on the length-width ratio of the PMOS transistors M1 and M4. Here, because the bandgap current IN1 is proportional to the temperature, the current IM4 is also proportional to the temperature. In addition, the first regulator circuit 312 receives the second bandgap voltage VN4 and generates a regulator current IR1, which is the second bandgap voltage VN4 divided by the resistor R1 (i.e., VN4/R1). Since the gate of the PMOS transistor M2 is connected to the gate of the PMOS transistor M3 and the source of the PMOS transistor M2 is also connected to the source of the PMOS transistor M3, the regulator current IR1 reflects the current IM3 on the PMOS transistor M3. The reflected current IM3 may or may not be the same as the regulator current IR1, depending on the length-width ratio of the PMOS transistors M2 and M3. Here, because the second bandgap voltage VN4 is inversely proportional to the temperature, the current IM3 is also inversely proportional to the temperature. The currents IM3 and IM4 form a temporary total current Itemp. The temporary total current Itemp is used to compensate for undesired temperature effect of the current-controlled oscillator 10. For example, by properly choosing the value of the resistor R1, when the oscillation frequency of the current-controlled oscillator 10 decreases as the temperature increases (as described in the FIG. 2 of related art), the temporary total current Itemp may be raised, providing more current IM6 (the detail is described later) to the current-controlled oscillator 10. With more current provided, the oscillation frequency of the current-controlled oscillator 10 is higher, thereby making up for the decrement of the oscillation frequency caused by the temperature offset.

However, the temporary total current Itemp may vary due to the tolerance of the resistor (the resistor tolerance may be as high as 20%). In light of this problem, a high-precision external resistor Rext is used in the second regulator circuit 316, as illustrated below.

The second regulator circuit 316 receives the temporary total current !temp from the PMOS transistor pair 314 and generates a voltage VR2 at an input of an operational amplifier thereof. Therefore, a voltage VRext which is equal to the voltage VR2 is generated at the external resistor Rext. Since the external resistor Rext is a high-precision resistor with little tolerance, there is minimal variation of the current IRext on the external resistor Rext. In addition, because the gate of the PMOS transistor M5 is connected to the gate of the PMOS transistor M6 and the source of the PMOS transistor M5 is also connected to the source of the PMOS transistor M6, the current IRext reflects the total current IM6 on the PMOS transistor M6. The reflected current IM6 may or may not be the same as the current IRext, depending on the length-width ratio of the PMOS transistors M5 and M6. The total current IM6 is the final current that is output and shared by the T-controller 31 and the PV-controller 32.

So far, description has been made concerning how the T-controller 31 prevents the current-controlled oscillator 10 from being affected by temperature deviations. In the following, the embodiment will illustrate how the PV-controller 32 prevents the current-controlled oscillator 10 from being affected by process and supply voltage variations.

FIG. 5A depicts a circuit diagram of a PV-controller according to an embodiment of the invention. The PV-controller 32 may comprise a third regulator circuit 320 and an adjust circuit 322. The third regulator circuit 320 comprises an operational amplifier, a PMOS transistor and a resistor R3. The operational amplifier has a first input receiving the first bandgap voltage VN1, a second input and an output. The PMOS transistor has a gate coupled to the output of the operational amplifier, a source coupled to the power supply and a drain coupled to the second input of the operational amplifier. The resistor R3 is coupled between the drain of the PMOS transistor and the ground. The adjust circuit 322 may comprise a PMOS transistor M7, an NMOS transistor M8 and a current mirror, as shown in FIG. 5A. The PMOS transistor M7 has a source coupled to the first bandgap voltage VN1, and a gate coupled to the resistor R3. The current mirror is coupled to the PMOS transistor M7. The NMOS transistor M8 has a drain coupled to the NX where the total current IM6 is provided, a gate coupled to the resistor R3, and a source coupled to the ground.

The components of the adjust circuit 322 may be dependent on the type of components within the current-controlled oscillator 10. Specifically, the current-controlled oscillator 10 may comprise only PMOS or NMOS transistors, or even both. If the current-controlled oscillator 10 comprises only a PMOS transistor, the corresponding PMOS transistor M7 will be required in the adjust circuit 322, as shown in FIG. 5B. If the current-controlled oscillator 10 comprises only an NMOS transistor, the corresponding NMOS transistor M8 will be required in the adjust circuit 322, as shown in FIG. 5C. Similarly, if the current-controlled oscillator 10 comprises both PMOS and NMOS transistors, the corresponding PMOS and NMOS transistors M7 and M8 are both required in the PV-controller 32, as shown in FIG. 5A. Referring to FIG. 5A, the PV-controller 32 receives the first bandgap voltage VN1 provided by the T-controller 31. Since the first bandgap voltage VN1 is not affected by PVT and the resistor tolerance, the voltage divided by the resistor R3 (divided voltage) is also not affected by PVT and the resistor. This provides a stable voltage difference between the gate and the source of the PMOS transistor M7 (i.e. VSG). As a result, the current IM7 on the PMOS transistor M7 is not affected by supply voltage variations (if the PMOS transistor M7 is connected to a supply voltage as a power supply, the current on the PMOS transistor M7 would suffer from supply voltage variations). Based on the same principle, the voltage difference between the gate and the source of the NMOS transistor M8 (i.e. VGS) is also stable.

Thus, description has been made concerning how the PV-controller 32 prevents the current-controlled oscillator 10 from being affected by supply voltage variations. In the following, the embodiment will illustrate how the PV-controller 32 prevents the current-controlled oscillator 10 from being affected by process variations. Referring to the following formulas:

I M 7 = μ p C ox ( W L ) ( V SG 7 - V TH 7 ) 2 for PMOS transistor M 7 , I M 8 = μ n C ox ( W L ) ( V GS 8 - V TH 8 ) 2 for NMOS transistor M 8 .

Based on the circuit structure of FIG. 5A, the gate-source voltage (VGS) of PMOS and NMOS transistors M7 and M8 is not affected by PVT and resistor tolerance. Therefore, the currents IM7 and IM8 are now dependent on the threshold voltage thereof (VTH). The magnitude of the threshold voltage VTH is dependent on the process variation of the MOS transistor. When the oscillation frequency of the current-controlled oscillator 10 is higher than a predetermined frequency (frequency shifting) due to a process variation of F (corner=F), the current IM7/IM8 is higher. This is because the process variation of F means a smaller threshold VTH, which results in a larger current IM7/IM8 that is shared from the total current IM6. With larger current IM7/IM8 shared from the total current IM6, the current provided to the current-controlled oscillator 10 is lower, further decreasing the oscillation frequency of the current-controlled oscillator 10. Note that the PV-controller 32 uses the same type of MOS transistor (P or N type of MOS transistor) as the current-controlled oscillator 10, so the process variation of F for the transistor within the current-controlled oscillator 10 also means the process variation of F within the PV-controller 32. Note that the description of the T-controller 31 and PV-controller 32 is completed.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

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Classifications
U.S. Classification331/176, 331/70, 331/66, 331/185, 331/108.00A
International ClassificationH03L1/00
Cooperative ClassificationH03B5/04, H03K3/011
European ClassificationH03K3/011, H03B5/04
Legal Events
DateCodeEventDescription
Oct 26, 2009ASAssignment
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WENG, MENG-CHIH;REEL/FRAME:023420/0804
Effective date: 20091023
Owner name: HIMAX TECHNOLOGIES LIMITED, TAIWAN